Magnetic hard disk drives are an example of information storage devices. Other information storage devices having some common or similar components or architecture include: magneto-optical disk drives, optical disk drives, tape drives, and removable media disk drives.
In magnetic recording applications, the head typically includes a slider and a magnetic transducer that comprises a writer and a read element. In optical recording applications, the head may include a minor and an objective lens for focusing laser light onto an adjacent disk surface. The slider is separated from the disk by a gas film that is typically referred to as an “air bearing.” The term “air bearing” is common because typically the gas is simply air. However, air bearing sliders have been designed for use in disk drive enclosures that contain alternative gases. For example, an inert gas like helium may be used because it does not degrade lubricants and protective carbon films as quickly as does oxygen. Helium may also be used, for example, because it has higher thermal conductivity than air, and therefore may improve disk drive cooling. Also, because the air bearing thickness depends on the gas viscosity and density, the air bearing thickness may be advantageously reduced in helium relative to air (all other conditions being the same). Furthermore, because helium has lower density than air, it may not buffet components within the disk drive as much, which may reduce track misregistration and thereby improve track following capability—facilitating higher precision in servo track writing and servo track following, which may enable increased data storage densities.
However, it may still be preferable for the disk drive to be air-filled during its operational lifetime. It is well known that disk drive enclosures that are designed to contain an alternative gas must be hermetically sealed to prevent an unacceptable rate of gas leakage, and such hermetic sealing may present additional design challenges and cost. For example, undesirable deflection of the top cover of the disk drive enclosure may occur with changes in barometric pressure in hermetically sealed disk drives. By contrast, such deflection may be mitigated in disk drives that contain air and so can include a breather filter that allows atmospheric air to bleed into or out of the disk drive enclosure through a breather port to equilibrate the internal pressure within the disk drive with the external ambient air pressure. Humidity may also be advantageously equilibrated via the breather port.
In many air-filled disk drive designs, the fluid communication between the interior of the disk drive and the external environment (through the breather filter and breather port) may also be required to pass through a narrow passage referred to as a “labyrinth path” in order to limit the rate of flow and/or diffusion. The term “labyrinth path” as used herein does not necessitate turns and bends; rather it refers to a narrow path that is longer than it is wide and restricts the rate of gas diffusion; it might have many turns and bends or it might be straight. The labyrinth may be part of the breather filter, or alternatively may be fabricated as a groove or depression in the base or cover.
One potentially advantageous trade-off that may be stricken between air-filled disk drive designs and alternative-gas-filled disk drive designs, is to (A) design the disk drive to operate as air-filled during its useful lifetime, for example so that it can employ a breather filter and breather port, but (B) temporarily fill the disk drive with an alternative gas like helium during a particular portion of the disk drive manufacturing process (e.g. servo track writing) that may benefit most thereby (e.g. from higher precision servo track positioning or a temporarily reduced flying height).
However, accomplishing this advantageous trade-off requires a practical method to fill and replace the gas within the disk drive enclosure in a high-volume manufacturing environment. One proposed method requires removal of the disk drive top cover, while another requires leaving open a large hole in the disk drive top cover, so that the gas inside may be changed quickly in serial fashion. However, according to such proposed methods the disk drive is in a condition unsuitable for use outside of an artificially clean environment (e.g. a clean room or clean hood). High-volume manufacturing operations that must be accomplished in clean rooms may be prohibitively burdensome and costly.
Certain proposed methods attempt to prevent leakage of an alternative gas from the disk drive during servo track writing. However, in that case if leakage of an alternative gas like helium occurs, such leakage may greatly exceed replacement by air, so that the pressure inside of the disk drive may unacceptably drop and/or cause deflection of the disk drive cover during servo track writing. Thus, there is a need in the art for improved structures and practical methods to accomplish servo track writing during temporary introduction of an alternative gas into the disk drive enclosure.